Thermal variable resistance device with protective sheath

ABSTRACT

A sensor and method of manufacturing a variable resistance sensor with a protective sheath that is cost effective and highly reliable, with stable resistance with an operating range of up to 1700° C. in hostile environments. The sheath is formed of highly stable dispersion hardened materials capable of withstanding mechanical loads and chemical attacks at elevated temperatures while maintaining internal chemical integrity.

CROSS-REFERENCE

This application is a continuation in part of and claims the benefit ofthe filing date of U.S. patent application Ser. No. 10/712,484 filedNov. 13, 2003 now U.S. Pat. No. 7,026,908.

FIELD OF THE INVENTION

The present invention relates to a device of which an electricalresistance will change in response to a change in surroundingtemperature, and more specifically to the construction of a sheathformed of a material exhibiting high mechanical strength for protectingthe device from physical damage.

BACKGROUND OF THE INVENTION

Conventional resistance temperature detectors (RTD), use a variety ofmaterials to produce elements with high operating temperatures. Thesematerials suffer from the detrimental effects of contamination, ionicmigration, sublimation, oxidation and substantial decrease in mechanicalstrength with increased operating temperatures. Current temperaturesensors are thus limited to an operating envelope of less than 650° C.(1200° F.) to ensure long term, stable output with minimum drift inresistance. Higher temperature devices can operate to temperatures up to850° C. (1562° F.) but are either limited to specific environmentalconditions (such as for instance: a vacuum environment, an inert gasenvironment, or a hydrogen atmosphere) and/or must be limited to shortterm operation to prevent premature failure. This temperature operatingrange has limited the application of these sensors in hostile, hightemperature systems such as those commonly encountered in the aerospace,petroleum and glass industries.

Even though the temperature measurement conducted by employing a RTD iswell known in the art, broad application of the RTD is still limited inhigh temperature hostile environments.

RTDs are useful temperature measuring devices which measure temperatureby employing a variable resistant material at a point where thetemperature is to be measured with lead ends connected to an instrumentwhich measures the amount of varying voltage when power is supplied tothe sensor. The resistant materials used for RTDs have been formed ofvarious metals which provide a varying resistance upon exposure tovarying heat.

Prior art temperature sensors have had the disadvantage of melting atfairly low temperature and have required insulation and varioussheathing systems to protect the sensor during operation at prolongedelevated temperatures. However, this sometimes results in undesirablereactions between the metals in the temperature sensor and the materialsused in the insulation and sheathing systems.

The problems of undesirable reactions in RTDs have been aggravated bythe temperatures encountered in nuclear reactor systems, rocketry heatsensors, high-temperature and vacuum processing and other applicationswhere temperature measurements at or above 1500° C. (2730° F.) areinvolved. RTDs have utilized sheathing and insulation in an effort toprevent the disintegration of the resistance material in such systems.The insulation and sheathing systems have the further disadvantage ofresulting in time delays in obtaining temperature readings due to theinsulation and mechanical packaging designed to prevent failureresulting from such problems as gas leakage at the RTD sheath seals,cracked sheaths and other mechanical limitations imposed by ceramicinsulated metal sheathed sensors.

Platinum, being chemically stable and having high temperature dependencyof electrical resistance, is employed as to a material for temperaturesensors, and specifically, for RTDs. In a conventional platinumtemperature sensor, a platinum wire is spirally wound on an insulator,or a platinum resistance pattern is formed as a thick or thin film on asubstrate.

Other high melting, noble metals such as rhodium (Rh), palladium (Pd),iridium (Ir) as well as precious metals such as gold (Au) and silver(Ag), and alloys thereof are known in the art. Such metals, however, arenot widely used because they are more susceptible to oxidation thanplatinum, and degrade by drift caused by selective oxidation.

Some of the characteristics of platinum can be improved by the usualalloy hardening method of adding a metal to the platinum base, followedby heat treatment. However, problems can occur after alloying. Forexample, when a high concentration of any alloying element is added tothe platinum base, the electrical properties of the resulting platinumlimb become inferior; at the same time the hardening phase willpartially or totally dissolve into the base at high temperatures, thusthe effects of the hardening action are reduced.

The prior art attempts to extend the operation range ofvariable-resistance temperature device have been limited to extendingthe range of known resistant materials through the use of insulationtechniques or increasing the high temperature properties of knownmaterials through alloying processes or coatings. The disadvantages ofthese techniques, including not reaching a high enough operatingtemperature, are discussed above. A significant benefit, however, isthat the conversion of the output signal generated by the knownresistant material is readily available through National Institute ofStandards and Technology (N.I.S.T.) or International ElectrotechnicalCommission (I.E.C.) standard tables.

Conversely, if a resistant material was chosen based on its desired hightemperature operating properties, and not based on providing a knownresistance output, then higher operating range variable-resistancetemperature device could be made, provided that the output signal of theresistant material is repeatable and convertible.

Dispersing oxides of transition metals or rare earth metals within nobleor precious metals is an example of a method of creating variableresistant material with the desired extended temperature properties. Forinstance, dispersion hardened platinum materials (Pt DPH, Pt-10% Rh DPH,Pt-5% Au DPH) are useful materials because they achieve very high stressrupture strengths and thus permit greatly increased applicationtemperatures than the comparable conventional alloys and are rugged.

Dispersion hardening (DPH) creates a new class of metal materials havingresistance to thermal stress and corrosion resistance that is evengreater than that of pure platinum and the solid solution hardenedplatinum alloys. When operational life, high temperature resistance,corrosion resistance and form stability are important, a sensor can bemanufactured of DPH platinum and can be used at temperatures close tothe melting point of platinum.

Dispersion hardened materials contain finely distributed transitionelement oxide particles which suppress grain growth andrecrystallization even at the highest temperatures and also hinder boththe movement of dislocations and sliding at the grain boundaries. Theimproved high temperature strength and the associated fine grainstability offer considerable advantages.

Platinum: Platinum-Rhodium Thermocouple Wire: Improved Thermal Stabilityon Yttrium Addition Platinum, By Baoyuan Wu and Ge Liu, Platinum MetalsRev., 1997, 41, (2), 81-85 is incorporated by reference. The Wu articlediscloses a process of dispersion hardening platinum for a platinum;platinum-rhodium thermocouple wire which incorporates traces of yttriumin the platinum limb.

As described in the Wu article, the addition of traces of yttrium toplatinum as a dispersion phase markedly increases the tensile strengthof the platinum at high temperature, prolongs the services life andimproves the thermal stability. Yttrium addition prevents the growth inthe grain size and helps retain the stable fine grain structure, as thedispersed particles of high melting point resist movements ofdislocations and make the materials harder. The strength of a materialis related to the movement and number of the dislocations.

In order to harden metals, the movement of the dislocations needs to berestricted either by the production of internal stress or by puttingparticles in the path of the dislocation. After the melting andannealing process, the majority of the trace yttrium (in the dispersionphase of the platinum) becomes yttrium oxide, which has a much highermelting point than platinum. When the temperature is near the meltingpoint, dispersion hardened particles fix the dislocation, thus hardeningthe platinum and increasing its strength.

At the same time the grain structure becomes stable after dispersionhardening and there is also microstructural hardening. The dispersedparticles affect the recrystallization dynamics, inhibit rearrangementof the dislocations on the grain boundaries and prevent the movement ofthe grain boundaries. Therefore, this dispersion hardened platinumpossesses a stable fine grain structure at high temperature.

This patent outlines a variable-resistance temperature sensor with aprotective sheath capable of protecting and extending the operatingrange of this class of sensor up to 1700° C. (3092° F.).

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide sensorwith a rugged sheath exhibiting high mechanical hardness for protectionof the sensor and/or conductors connected thereto.

Accordingly, it is another object of the present invention to provide anextended temperature range thermal variable resistance device withenhanced high temperature operating characteristics and long term,stable output and minimum drift in resistance.

Another object of the present invention is to provide an extendedtemperature range thermal variable resistance device that can beconfigured as a resistance temperature device for the purpose ofmeasuring localized temperature. Yet another object of the presentinvention is to provide an extended temperature range thermal variableresistance device which in dual mode operation can be implemented as aheat flux sensor.

Still another object of the present invention is to provide a thermalvariable resistance device implementing electronics to condition theoutput and convert it to specified calibrated reference data, or to anindustry standard such as a National Institute of Standards andTechnology reference or an International Electrotechnical Commissionreference.

Yet another object of the present invention is to provide a method forthe production of a cost effective, high reliability, stable resistancedevice with an operating range of up to 1700° C. (3092° F.) in hostileenvironments.

These and other objects of the present invention are achieved in oneadvantageous embodiment by a sensor comprising a resistor deposited on asubstrate, the resistor exhibiting a change in resistance with a changein ambient temperature, and a first conductor formed from a firstconductor material, the first conductor electrically connected to theresistor. The sensor further comprises a second conductor formed from asecond conductor material, the second conductor electrically connectedto the resistor, and a sheath enclosing at least the resistor, thesheath formed of a sheath material having at least one noble metal andan oxide selected from the group consisting of yttrium oxide, ceriumoxide, zirconium oxide, and combinations of these.

It is contemplated that virtually any standard thermal resistive devicemay effectively be utilized in connection with the sheath comprising theabove-described sheath material.

In another advantageous embodiment a method for manufacturing a sensoris provided comprising the step of positioning a resistor formed from aresistor material on a substrate. The method further comprises the stepsof electrically connecting a first conductor to the resistor, the firstconductor formed from a first conductor material, and electricallyconnecting a second conductor to the resistor, the second conductorformed from a second conductor material. The method still furthercomprises the steps of forming a sheath of a material having at leastone noble metal and an oxide selected from the group consisting ofyttrium oxide, cerium oxide, zirconium oxide, and combinations of these,and enclosing at least the resistor within the sheath.

In still another advantageous embodiment a sensor is provided comprisinga resistor exhibiting a change in resistance with a change in ambienttemperature. The sensor further comprises a first conductor formed froma first conductor material, the first conductor electrically connectedto the resistor, and a second conductor formed from a second conductormaterial, the second conductor electrically connected to the resistor.The sensor still further comprises a sheath enclosing at least the firstand second conductors, the sheath formed of a sheath material having atleast one noble metal and an oxide selected from the group consisting ofyttrium oxide, cerium oxide, zirconium oxide, and combinations of these.

In yet another advantageous embodiment a sensor is provided that isresistant to degradation at high temperature having a resistor formedfrom at least one noble metal and an oxide. The oxide may in oneadvantageous embodiment, comprise yttrium oxide, cerium oxide, zirconiumoxide, and limited combinations of these and is disposed on a substrate.The sensor having at least a first and second lead connected to theresistor for transmitting an electrical signal. The resistor may forinstance, be wound around the substrate or deposited on said substrate.

In still another advantageous embodiment a method for manufacturing asensor is provided comprising the steps of positioning a resistor formedfrom a resistor material on a substrate, electrically connecting a firstconductor to the resistor, the first conductor formed from a firstconductor material, and electrically connecting a second conductor tothe resistor, the second conductor formed from a second conductormaterial. The method further comprises the steps of forming a sheath ofa material having at least one noble metal and an oxide selected fromthe group consisting of yttrium oxide, cerium oxide, zirconium oxide,and combinations of these, and enclosing at least the first conductorand the second conductor within the sheath.

The objects of the present invention are further achieved in anotherembodiment by providing a sensor which is resistant to degradation athigh temperature having a resistor formed from an oxide. The oxide mayin one advantageous embodiment, comprise the transition element oxidesand rare earth metal oxides, and combinations of these, where the oxideis dispersion hardened within the grain boundary and within the basematerial of at least one base metal. The base metal may in oneadvantageous embodiment, comprise the noble metals and the preciousmetals, and combination of these, and is disposed on a substrate. Thesensor having at least a first and second lead connected to the resistorfor transmitting an electrical signal.

The objects of the present invention are achieved in yet anotherembodiment by a method of manufacturing a high temperature resistantsensor by forming a resistor from at least one noble metal and an oxideselected from the group consisting of yttrium oxide, cerium oxide,zirconium oxide, and combinations of these. The method further comprisesthe step of disposing the resistor on a substrate by either winding theresistor around the substrate or by depositing the resistor on thesubstrate. Finally, the method comprises the step of attaching at leasta first and second lead to the resistor for transmitting an electricalsignal.

The objects of the present invention are further achieved in anotherembodiment by providing a sensor which is resistant to degradation athigh temperature having a resistor that is formed from an oxide selectedfrom the group consisting of yttrium oxide, cerium oxide, zirconiumoxide, and combinations of these, said oxide dispersion hardened withinthe grain boundary of platinum and is disposed on a substrate. Thesensor also having at least a first and second lead connected to theresistor for transmitting an electrical signal and a transducer.

The objects of the present invention, in each of the above describedembodiments, could be further achieved where an electrical signalcomprises a varying voltage and is applied to a transducer. Thetransducer may be a temperature measuring device. The output of thetransducer may correlate to a temperature or a logic function applied tospecific calibration data to determine the temperature. The transduceroutput could correlate to a standard reference output, or couldcorrelate specifically to a National Institute of Standards andTechnology or to an International Electrotechnical Commission reference.

In still another advantageous embodiment a modular sensor system forgenerating and sending a signal from a sensor to a transducer isprovided comprising a sensor for generating a signal having a substrateand a resistor, disposed on the substrate, formed from at least onenoble metal and an oxide selected from the group consisting of yttriumoxide, cerium oxide, zirconium oxide, and combinations of these, theresistor further having first and second conductors electricallyconnected thereto. The system further comprises a transmit lead modulefor transmitting the signal to the transducer, the transmit lead modulehaving a first transmit lead electrically connected to the firstconductor, and a second transmit lead electrically connected to thesecond conductor, the second transmit lead comprising a differentmaterial than the first transmit lead. The transmit lead module also hasan insulating layer within which the first transmit lead and the secondtransmit lead are located, and an outer layer within which theinsulating layer is located.

In yet another advantageous embodiment a modular sensor system forgeneration of a signal by a sensor and for sending of the signal viafirst and second electrical conductors to a transducer is providedcomprising, a transmit lead module for transmitting the signal to thetransducer. The transmit lead module has a first transmit leadelectrically connected to the first conductor, and a second transmitlead electrically connected to the second conductor. The transmit leadmodule further has an insulating layer within which the first transmitlead and the second transmit lead are located, and an outer layer withinwhich the insulating layer is located, the outer layer comprising thesame material as said first transmit lead.

The invention and its particular features and advantages will becomemore apparent from the following detailed description considered withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one advantageous embodiment of the presentinvention.

FIG. 1A is a block diagram of another advantageous embodiment of thepresent invention according to FIG. 1.

FIG. 1B is a block diagram of still another advantageous embodiment ofthe present invention according to FIG. 1.

FIG. 2 is an illustration of yet another advantageous embodiment of thepresent invention according to FIG. 1.

FIG. 2A is an illustration of a transmit lead module according to FIG.2.

FIG. 3 is a block diagram of a component configuration according to FIG.2.

FIG. 4 is a block diagram of another component configuration accordingto FIG. 2.

FIG. 5 is an illustration of the resistor wound around the substrateaccording to one advantageous embodiment illustrated in FIG. 2.

FIG. 6 is a block diagram of still another advantageous embodiment ofthe present invention.

FIG. 7 is a block diagram of yet another advantageous embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like reference numerals designatecorresponding structure throughout the views.

FIG. 1 is a block diagram illustrating one preferred embodiment of thepresent invention showing sensor 10. A substrate 12 is shown in contactwith a resistor 11. Also shown are first conductor 23 and secondconductor 24 electrical both of which are shown connected to resistor11.

Sensor 10 is further illustrated in FIG. 1 with insulation 21. Theinsulation may comprise any suitable insulating material desiredincluding but not limited to a refractory ceramic material such as forinstance, Al₂O₃ or MgO. Although insulation 21 is shown in FIG. 1enclosing sensor 10, it is contemplated that insulation 21 may onlyenclose a portion of sensor 10, such as for instance, first and secondconductors 23, 24 or resistor 11, or any other portion thereof.

Also illustrated in FIG. 1 is sheath 20 shown enclosing insulation 21.Sheath 20 may comprise, for instance, a noble metal such as a platinumgroup metal, and a metal oxide selected from the group consisting ofyttrium oxide, cerium oxide, zirconium oxide, and combinations of these.It is further contemplated that through an annealing process calleddispersion hardening, the metal oxides may be deposited within the grainboundaries and main body of the noble metal. This process produces asheath 20 formed of a highly stable material capable of withstandingmechanical loads and chemical attacks at elevated temperatures whilemaintaining its internal chemical integrity. This is highly desirableespecially in hostile environments where the sensor is subjected tomechanical stress and/or a wide range of temperatures.

In one preferred embodiment sheath 20 comprises platinum, having yttriumoxide or yttrium and zirconium oxide dispersed within its grain boundaryand within the main bodyportion. In another preferred embodiment thesheath 20 comprises a platinum rhodium alloy (10% rhodium) havingyttrium oxide or yttrium and zirconium oxide dispersed within its grainboundary and within the main body. Although sheath 20 is shown in FIG. 1enclosing sensor 10, it is contemplated that sheath 20 may only enclosea portion of sensor 10, such as for instance, first and secondconductors 23, 24 (FIG. 1A) or resistor 11 (FIG. 1B) or any otherportion thereof.

It is contemplated that virtually any standard thermal resistive devicemay effectively be utilized as resistor 11 in connection with sheath 20comprising the above-described sheath material.

Still further illustrated in FIG. 1 is transmit lead module 30 thatincludes transmit leads 13, 14. Also illustrated in FIG. 1 is transmitlead module insulation 21′ enclosing transmit leads 13, 14. Transmitlead module insulation 21′ may comprise any material as previouslydescribed in connection with insulation 21. Further illustrated istransmit lead module sheath 20′, which encloses transmit lead moduleinsulation 21′. Transmit lead module sheath 20′ may also comprise anymaterial as previously described in connection with sheath 20. It isfurther contemplated that, although only one transmit lead module 30 isshown in FIG. 1, any number may be connected together, for instance inan end-to-end fashion, as required depending upon the installation.

Referring now to FIGS. 2-5, a sensor 10, is made with a resistor 11 of aclass of materials chosen to be resistant to degradation in hightemperature operation up to 1700° C. (3090° F.) and deposited on and/oraround a substrate 12. The class of materials is made up of one or morebase metals, usually a noble metal, with metal oxides. In oneadvantageous embodiment the metal oxides may comprise yttrium oxide,cerium oxide, zirconium oxide, and combinations of these. Through anannealing process not described herein, the metal oxides may bedeposited within the grain boundaries and main body of the base metal.The process is called dispersion hardening. This has the effect ofstabilizing the grain structure of the material at extended temperaturesand provides an increased resistance path for impurities. The net effectis a highly stable material capable of withstanding mechanical loads andchemical attacks at elevated temperatures while maintaining its internalchemical integrity. This provides the foundation for an extendedtemperature variable resistance device with long term, stable output andminimum drift in resistance.

The base metal may be chosen from the noble metals such as for instance,the platinum group metals. It is preferable that the resistor 11 be madeof platinum or Pt/Rh, having yttrium oxide or yttrium and zirconiumoxide dispersed within its grain boundary. However, it is foreseeablethat the resistor could be formed from an oxide from the groupconsisting of the transition metals or the rare earth metals, or acombination thereof, dispersion hardened within the grain boundary of abase and main body metal consisting of the noble metals or the preciousmetals, or combinations thereof.

The resistor 11, with any across sectional geometry, may be wound arounda nonconductive, high temperature substrate to a predeterminedresistance value. (See FIG. 5). Similarly the resistor material can bedeposited on a substrate to form an element of desired resistance.(FIGS. 2-4). The size of the resistor is dictated by the requiredresistance, cross sectional geometry of the resistor material andcoefficient of electrical resistance of the resistor material.

The substrate may be made from the same class of material as theresistor, having at least one noble metal with a metal oxide from thegroup consisting of yttrium oxide, cerium oxide, zirconium oxide, andcombinations of these, dispersed within its grain boundary. Refractorymaterials or one of the base materials coated with a high temperatureinsulator of varying compositions such Al₂O₃ or MgO may also be used asthe substrate. The substrate may also be formed with a thin insulatingcoating from at least one noble metal with a metal oxide from the groupconsisting of yttrium oxide, cerium oxide, zirconium oxide, andcombinations of these.

In one advantageous embodiment, electrical leads 23, 24 for transmittingan electrical signal, may be electrically connected between resistor 11and a transducer/conditioner 15. In addition, transmit leads 13, 14 maycomprise different material compositions than the electrical leads 23,24 creating a junction at 17, 18. Another possible junction point 25, 26may comprise still another differing material composition than thetransmit leads 13, 14. However, the sensor could be formed such that oneor both of the wire components may transmit the electrical signal to thetransducer/conditioner 15. It should also be noted that the electricalsignal may be electrically compensated for these junction points ofdiffering compositions.

The resistor may also be housed in a sheath 20 to protect it from thehostile environments in which the sensor operates. The sheath 20 may beformed of a high temperature alloy or made from the same class ofmaterial as the resistor, having at least one noble metal with a metaloxide from the group consisting of yttrium oxide, cerium oxide,zirconium oxide, and combinations of these, dispersed within its grainboundary.

The sensor may be insulated between the resistor 11 and the sheath 20.The insulation 21 may be a refractory material such as Al₂O₃ or MgO.(FIG. 2).

In operation, the resistor is exposed to a temperature gradient ΔT. Theresistance value of the resistor varies in response to the temperaturegradient. A power source is applied to the sensor and activates thesensor. The power source may be, for instance, a constant current. Anelectric signal is generated, which may be, for instance, a varyingvoltage. The varying voltage may be a function of the temperaturegradient and the varying resistance of the resistor. The electricalsignal is then transmitted to transducer 15.

In one advantageous embodiment illustrated in FIG. 2, electrical leads23, 24 terminate at junctions 17,18 respectively. From junctions 17,18transmit leads 13, 14 extend to junction point 25, 26 to terminate attransducer/conditioner 15. In FIG. 2, transmit leads 13, 14 areillustrated located inside transmit lead module 30.

The structure and method for manufacturing transmit lead module 30 inone advantageous embodiment as illustrated in FIG. 2A, will now bedescribed. Transmit lead module 30 generally comprises: transmit leads13, 14; insulating layer 32; and outer layer 34. Transmit leads 13, 14may comprise any suitable materials as previously described herein inconnection with FIG. 2. Insulating layer 32 may comprise, for instance,a refractory ceramic material such as Al₂O₃ or MgO generally formed intoan elongated member, such as for instance, a cylinder. Also illustratedin FIG. 2A are two through holes 36, 38 extending axially through thelength of insulating layer 32 through which transmit leads 13, 14 arerespectively inserted. Surrounding and encasing insulating layer 32 isouter layer 34. Outer layer 34 may comprise in one advantageousembodiment, the same material as one of transmit leads 13, 14. Oneadvantage realized from this particular configuration is that one of theelectrical lead/transmit lead junctions may be eliminated.

Once the insulating layer 32 containing transmit leads 13, 14 isinserted into outer layer 34, the entire transmit lead module 30 may beswaged. The compression of transmit lead module 30 causes insulatinglayer 32 to be compressed and tightly crushed such that air is evacuatedand any air pockets within transmit lead module 30 may be effectivelyeliminated.

Any number of transmit lead modules 30 may then be tied togetherdepending upon the distance between the sensor and thetransducer/conditioner 15. This provides versatility and modularity tothe system as the installer may utilize any number of transmit leadmodules 30 in an installation. Transmit lead modules 30 may further bebent and manipulated as desired to custom fit a particular installation.The outer layer 34 being rigid further provides protection for transmitleads 13, 14 from wear, abrasion and repeated bending and/or flexing.This will increase the effective lifespan of the system. In addition, aspreviously discussed, transmit lead modules 30 may be joined togetherwith each other in an end-to-end fashion with transmit leads 13, 14 inthe first transmit lead module 30 forming a junction with transmit leads13, 14 in the second transmit lead module 30. However, when the exteriorlayer 34 for both the first and second transmit lead modules 30comprises the same material as one of the transmit leads 13, 14, thenthe corresponding transmit lead junction may be eliminated furthersimplifying the system.

In one advantageous embodiment, the sensor may be configured as aResistance Temperature Detector (RTD) for the purpose of measuringlocalized temperature averaged over the surface of the active area. Theoutput from the transducer would then be a temperature reading from atemperature measuring device 16. (FIG. 3). Certain reference conversionsexist to determine temperature from a varying voltage output from a RTD.These standards are determined by such agencies as the NationalInstitute of Standards and Technology and the InternationalElectrotechnical Commission. The standards are based upon the propertiesof the material of the resistor and the temperature ranges to which theRTD is subjected.

No standard reference to correlate the varying voltage to a temperaturereading is available for the class of materials used in the presentinvention. Accordingly, a logic function 17 (FIG. 4) can be applied tothe varying voltage to convert it to one of the known industrystandards. This would make the RTD an off the shelf component.

The output of the sensors need not be converted to an NIST standard tomake it usable. In some applications, calibration data can be suppliedalong with a basic algorithm which would be implemented in a controlsystem developed by an outside source. In this case the algorithms wouldbe customized to the user's particular application.

In dual mode operation, the sensor could be implemented as a heat fluxsensor.

While not shown, it should be noted that resistor 11, wound around thenonconductive, high temperature substrate as illustrated in FIG. 5, mayalso effectively be utilized with temperature measuring device 16 andlogic function 17. (FIGS. 3 and 4).

FIGS. 6 and 7 are similar to FIG. 2 comprising a sensor 10 having aresistor 11 deposited on and/or around substrate 12 with an insulation21 located between resistor 11 and sheath 20 and further comprisingtransducer/conditioner 15.

FIG. 6 differs from FIG. 2 in that three electrical leads (47, 48, 49)are electrically connected to resistor 11. FIG. 6 further comprisestransmit lead module 40, which also is configured with three transmitleads (50, 51, 52) forming junctions (41, 43, 45) where electrical leads(47, 48, 49) and transmit leads (50, 51, 52) meet and junctions (42, 44,46) where transmit leads (50, 51, 52) meet transducer/conditioner 15. Avariable voltage may then be measured across any combination of theseleads.

Another alternative embodiment is illustrated in FIG. 7 which is similarto FIG. 6 except four electrical leads (69, 70, 71, 72) are electricallyconnected to resistor 11. FIG. 7 further comprises transmit lead module60, which also is configured with four transmit leads (73, 74, 75, 76)forming junctions (61, 63, 65, 67) where electrical leads (69, 70, 71,72) and transmit leads (73, 74, 75, 76) meet and junctions (62, 64, 66,68) where transmit leads (73, 74, 75, 76) meet transducer/conditioner15. A variable voltage may then be measured across any combination ofthese leads.

While various combinations, i.e. two leads (FIG. 2), three leads (FIG.6), and four leads (FIG. 7), have been illustrated herein, it iscontemplated that any varying number of leads may advantageously beutilized in connection with the present invention.

Those skilled in the art may tailor the present invention to suit aparticular requirement. It will be understood that these or other typesof changes and substitutions may be made within the spirit and scope ofthe invention as defined in this claim.

1. A sensor for measuring temperature comprising: a resistor on asubstrate, said resistor exhibiting a change in resistance with a changein ambient temperature; a first conductor formed from a first conductormaterial, said first conductor electrically connected to said resistor;a second conductor formed from a second conductor material, said secondconductor electrically connected to said resistor; and a sheath,electrically insulated from and enclosing both said first and saidsecond conductors, said sheath extending along a longitudinal length ofsaid first and second conductors to protect said conductors; said sheathformed of a sheath material having at least one noble metal and an oxideselected from the group consisting of yttrium oxide, cerium oxide,zirconium oxide, and combinations of these.
 2. The sensor of claim 1wherein the first conductor material and the second conductor materialare different than the sheath material.
 3. The sensor of claim 1 whereinsaid resistor comprises noble metal and an oxide selected from the groupconsisting of yttrium oxide, cerium oxide, zirconium oxide, andcombinations of these.
 4. The sensor of claim 1 wherein the noble metalis a platinum group metal.
 5. The sensor of claim 4 wherein the noblemetal is platinum.
 6. The sensor of claim 5 wherein the oxide isdispersion hardened within grain boundaries and a main body portion ofthe platinum.
 7. The sensor of claim 4 wherein the noble metal isplatinum rhodium alloy.
 8. The sensor of claim 7 wherein the oxide isdispersion hardened within grain boundaries and a main body portion ofthe platinum rhodium alloy.
 9. The sensor of claim 7 wherein theplatinum rhodium alloy is Pt-10% Rh.
 10. A sensor for measuringtemperature comprising: a resistor exhibiting a change in resistancewith a change in ambient temperature; a first conductor formed from afirst conductor material, said first conductor electrically connected tosaid resistor; a second conductor formed from a second conductormaterial, said second conductor electrically connected to said resistor;and a sheath electrically isolated from said first and secondconductors, said sheath enclosing at least said first and secondconductors and formed of a sheath material having at least one noblemetal and an oxide selected from the group consisting of yttrium oxide,cerium oxide, zirconium oxide, and combinations of these, said sheathextending along a longitudinal length of said first and secondconductors to protect said conductors.
 11. The sensor of claim 10wherein the first conductor material and the second conductor materialare different than the sheath material.
 12. The sensor of claim 10wherein the noble metal is platinum.
 13. The sensor of claim 12 whereinthe oxide is dispersion hardened within grain boundaries and a main bodyportion of the platinum.
 14. The sensor of claim 10 wherein the noblemetal is platinum rhodium alloy.
 15. The sensor of claim 14 wherein theoxide is dispersion hardened within grain boundaries and a main bodyportion of the platinum rhodium alloy.
 16. The sensor of claim 14wherein the platinum rhodium alloy is Pt-10% Rh.
 17. A method formeasuring temperature with a sensor comprising the steps of: positioninga resistor in an area to measure an ambient temperature, the resistorhaving a first conductor electrically connected thereto formed of afirst conductor material and a second conductor electrically connectedthereto formed of a second conductor material, the first and secondconductors electrically insulated from and enclosed in a sheath of amaterial having at least one noble metal and an oxide selected from thegroup consisting of yttrium oxide, cerium oxide, zirconium oxide, andcombinations of these, the sheath extending along a longitudinal lengthof the first and second conductors to protect the conductors; developinga change in resistance across the first and the second conductorsconnected to the resistor when the ambient temperature changes;monitoring the change in resistance to determine the change in ambienttemperature.
 18. The method of claim 17 wherein the first conductormaterial and the second conductor material are different than the sheathmaterial.
 19. A sensor for measuring temperature comprising: a resistoron a substrate, said resistor exhibiting a change in resistance with achange in ambient temperature, said resistor comprising a noble metaland an oxide selected from the group consisting of yttrium oxide, ceriumoxide, zirconium oxide, and combinations of these; a first conductorformed from a first conductor material, said first conductorelectrically connected to said resistor; a second conductor formed froma second conductor material, said second conductor electricallyconnected to said resistor; and a sheath enclosing said first and saidsecond conductors, and said resistor, said sheath formed of a sheathmaterial having at least one noble metal and an oxide selected from thegroup consisting of yttrium oxide, cerium oxide, zirconium oxide, andcombinations of these, said sheath extending along a longitudinal lengthof said first and second conductors to protect said conductors.